Telephone trunking system.



J. W. LATTIG dz 0. L. GOODRUM. TELEPHONE TRUNKING SYSTEM.

APPLIUAT'ION FILED 06123. 1903.

wi l mmlw will 11:1llainllnllllllwlllaih Q PATENTED AUG. 21. 1906.

UNITED STATES im'rENfr ora ion.

JACOB WILLIAM LATTIG, OF WYNUOTE, AND CHARLES LANE GOODRUM, F PHILADELPHIA, PENNSYLVANIA, ASSIGNORS TO EASTERN TELE- PHONE MANUFACTURING COMPANY, OF WEST CHESTER, PENNSYL- VANIA, A UURPORATlON OF PENNSYLVANIA.

TELEPHONEv TRUNKING- SYSTEM.

Specification of Letters .E'atent.

Patented Aug. 21, 1906.

so all w/wm/ zit may concern:

Be it known that we, JACOB WrLLIAM LATTIG, residing at \Vyncote, Montgomery county, and CHARLES LANE GoonRUM, residing at Philadelphia, county of Philadelphia, Pennsylvania, citizens of the United States, have invented a certain new and useful Improvement in Telephone Trunking Systems, of which the following is a specification.

Our invention relates to telephone-exchange systems, and more particularly to such systems as employ a common battery or batteries located at each central of'lice for the purpose of signaling to and from the exchange. It has for its object the provision of means whereby the trunk connections between different portions of the same exchange or between different exchanges may be more erfectly controlled and the work more easi y and certainly accomplished than heretofore.

In all exchange-work efhciency of operation is the 0nd constantly sought. Assuming that metallic circuits are employed with standard apparatus, so that satisfactory talking conditions are assured, improvements in efficiency must contemplate the connection and disconnection of subscribers either in the same time with less laborer in less time with the same labor, or both in less time and with less labor. Since the general adoption of common batteries supplying energy from the central ofiices for all purposes, it has been found possible to employ automatic sig nals which by their display or concealment inform the operators accurately not only of the condition of the circuits with which they are working, but as to the acts of the subscribers they are connecting and of other operators who may be assisting in making the connections. In our previous patent, No. 722,367, dated March 10, 1903, and reissued September 8, 1903, as No. 12,156, we have described and claimed a common-battery system employing such automatic signals for the subscribers lines and in connection with the cord-circuits. The cord-circuit or supervisory signals are depended upon by a subscribers operator to indicate the condition of 5 the subscribers lines during connection.

When a call has been made, the supervisory signal corresponding to the calling-plug indi- 1 cates when the called subscriber answers. In transferring a connection through a trunk line to another 0 )erator whether in the same or a distant exchange, however, it has not been found practicable heretofore to depend entirely upon the supervisory signals at the answering or initiating switchboard-section. In many cases systems have been installed wherein the responsilulity is divided between the subscribers or A' operator and the trunk or B operator, the former initiat ng the trunk connection and the latter then assuming supervision and control over the same. Such a practice is not productive of the highest cfhciency, inasmuch as the A operators work lacks uniformity and the failure of instant ccoperation between the operators may result in delays or in the calling-line being temporarily hung u In order to prevent such miscarriages, w ich are especially liable to occur where the traflic is heavy, elaborate arrangements of trunk-signaling have been devised which a re not only cumbersome in themselves but 1 y introducing new combinations only increase the complexity of the operations they are meant to simplify.

According to our present invention we im pose upon the A operator the entire re sponsibility for every connection, so arranging the trunk connections that her ordinary supervisory signals may be depended upon for all necessary information whether in a simple connection or in trunking, and by the provision of simple means we enable the A operator to control, as well as supervise, the B operator's work. To this end and without being necessarily restricted to our system above mentioned we arrange the supervisory signals at the A" operators station, so that in trunking they can be affected by the main battery at the 'B" opcrators station, the currentflow therefrom being determined by the insertion of the trunk-plug at the 13" end and by the called subscriber, and we arrange a signal in the trunk at the 13 end adapted to take current from the main battery at that end, the flow of said current being determined by the insertion in or withdrawal from the trunk-jack of the A operators calling-plug. By this arrangement the A operators work is rendered uniform,

as she not only supervises all connections, but also rings up the called subscriber in every case and effects the disconnection. in every case in response to the usual signals.

Our invention is susceptible of application to any system employing a bridged battery,

and by installing such a battery it may be applied even to magneto systems. As a matter of convenience we have shown and shall describe it in connection with the circuits of our aforesaid patent but it is understood that we are not limited thereto.

Our invention is illustrated in the accompanyin drawing, wherein the figure is a dia gram siowing two switchboards A and B, with the operators apparatus and an interconnecting trunk-line.

Referring to the drawing, X is a subscribers telephone-station connected to the central station A by line-wires 1 and 2. At station X are provided the usual pieces of a paratus, comprising the transmitter T, tie receiver T, the polarized bell Q, the condenser C, and the switch-hook H. The linewires 1 and 2 pass to the central office and there by means of extensions 3 and 4 are con nected to the terminal bus-bars 5 and 6 of the main battery A. interposed between the line and the bus-bars are the impedancecoils I and I, which serve to limit the current-flow in the line and also to prevent the passage of voice-waves over the bus-bars 5 and 6. Connected in the No. 1 side of line is the relay R, whose armature 1 controls the circuit 19 of the line signal-lamp L. Connectcd to line outside of this relay are the multiple jacks J, each having a pair of springs j j and a sleeve-contact or thimble Each spring is connected to the No. 1 side of line, and each spring 7' is connected to the extension 3 between the relay R and the im pedancecoil I. Each thimble 7' is connected to the No. 2 side of line. When a plug is inserted in any of these jacks, the relay R is short-circuited at the springs j by the tip of the plug.

The organization of circuits and apparatus at subscribers station Y and thence to the central ofiice B is the same as that just described. The line-jacks at oflice B are lettered J and the main battery is B.

It will be understood that in the diagram we have shown a single subscribers station X and its line leading to the central oflice, with the terminal apparatus 3 but this is sup posed to be multipied as many times as there are subscribers connected to that exchange. We have shown jacks J representing the terminals of an additional subscribers line, which is sup osed to be connected in similar manner to (lie line 1 2. In order to connect these lines for conversation, the subscribers operator is provided with the usual complement of cords, plugs, and auxiliary apparatus, one set of which is illustratcd. Plugs P and P are united by the cord conductors 8 10 and 9 11, each side of the cord being inductively continuous for alternating currents, but conduetively discontinuous for direct currents by reason of the inclusion of condensers C and C The main battery A, in addition to its terminal bus-bars 5 and 6, is provided with an intermediate bus-bar 7, connected at such a point as to render the differences of poten tial unequal, or, in other words, the battery is organized in two divisions or sections a and a, as fully described in our patent hereinbefore referred to. Connected by conductors 12 and 13 between the cord conductor 9 and the bus-bar 7 is the polarized supervisory relay R, and similarly connected by wires 12 and 14 between the bus-bar 7 and the cord conductor 11 is the polarized supervisory relay R The armature r of relay R is normally drawn to the right by a retractile spring aided by the ermanent magnetism, and when moved to t e left against the tension of the spring it closes the circuit 15 17 of the su ervisory lamp L. The armature 1' of the re ay R in a similar manner controls the circuit 16 17 of the supervisory lamp L In connection with. the cord-circuit the key K serves to connect the operators telephone 0 for testing and listening in the usual manner, while the key K is the ordinary ringing-key, which breaks the cord conductors 10 1]. and connects the calling-generator to the plug P.

The ordinary operation of the system thus far described is fully set forth in our patent above referred to and therefore it need not be given here in detail. Briefly outlined, it is as follows: Subscriber X calls by taking down his receiver, whereupon the current-fiow in his line from the battery A energizes the relay R and lights the lamp L. The insertion of answering-plug P short-circuits the relay and puts out the amp, at the same time connecting the supervisory relay R in the following circuit: battery-section a, bus-bar 7 wire 12, relay R, wires 13 and 9, sleeve of plug and thimble j of the jack, wire 4, busbar 5, and back to the battery. As the subscribers circuit is closed a branch is also closed from the thimble 7' by way of linewire 2 to the subscriber's station, back by line-wire 1 to the bus-bar 6 and battery-section a. The difference of potential between the bus-bar 7 and the ack-thimble j will be the algebraic sum of the potential differences due to the sections a and a acting against each other, and the resultant current-flow through the relay-windings will keep the ar mature T in its normal or inoperatlve position. Su posing the desired connection to be with t e jack J key K is closed and the tip of plug P is applied to the thimble of jack J to make the busy test. If the line is idle, the tip and the jack-thimble 3' will be at the same potential; but if the line is busy the jack-thimble will be connected back through another cord conductor 11 to the bus-bar 7, and a click will be heard in the receiver. In testing the tip of the plug is connected through the key K andthe operators set by wire 18 and through coil I to the bus-wire 5, to which the sleeve 7' of each jack is also connected through wire 4 and coil 1. When a line is busy, all the test-thimbles j of that line are connected through the plug that is in through its cord conductor 9 or 11 through the corresponding supervisory relay and wire 12 to bus-wire 7. Such a connection therefore raises the potential of the testthimbles with respect to the plug-tip by just the ifi'erence between bus-wires 5 and 7 due to the battery-section a. Assuming the former to be the case, the plug P is fully inserted in the jack, thereby closing the circuit 12, 14, 11, j", 20, 25, and 5 of the relay R, which thereupon lights the lamp L The ringing-key K is then used to call the subscriber and upon his answering the lamp L goes out, as in the ease of the calling subscriber.

In case the wanted line is connected to another exchange or to another switchboard in the same exchange it will be necessary to trunk the connection. Suppose, for example, subscriber Y, connected to exchange B,

is wanted. For the purpose of such connections trunk-lines are provided typified by a single circuit in the diagram. Trunk-line 2O 21 extends from central station A to central station B, terminating at the former in the trunk-jack J and at the latter in the plug P The thimble j of the jack J is connected through conductor 20 to the sleeve of the plug P and the spring 7' of the jack is connected by conductor 21 to the tip of the plug. When not in use, the'spring 7' rests upon an anvil j to short-circuit or cross the two sides of the trunk-line together.

At station B we interpose in the trunkconductor 21 a relay R whose armature r controls the local circuit 23 of the trunk sig nal-larnp L supplied by a battery B which may be common to a considerable number of circuits, as indicated by the short branch lines shown. In order that the relay-winding may not impede the transmission of speech-waves or of the alternating ringingeurrent, we preferably provide a shunt 22, containing a suitable condenser C Accompanying each grou of trunk-lines between the stations A and we provide an operator's instruction-circuit 24, connected to the B operators telephone 0 and adapted to be connected to the A operators telephone 0 in any suitable manner, as by the key K The operation of the complete system thus described where a connection is to be trunked is as follows: Suppose subscriber X to have called and that he has been answered by the A o erator, as already described. Suppose su scriber Y to he wanted. The A" operator connects herself with the B operator and repeats the number wanted. The B operator answers by designating the trunk to be used. Assuming this to be the trunk 20 21, the A operateor inserts the plug P in jack J thereby separating spring 7' from the anvil j and connecting cord conductors 10 11 to the trunk-conductors 21 and 20, respectively. This produces no effect on the supervisory relay R The B operator then takes up the plug I and inserts it in a jack J of subscriber Y's line. It should be observed that the intermediate bus-bar .7 at each central station is grounded. Hence the insertion of the plug I immediately completes a circuit for the supervisory relay R at sta tion A, as follows: Battery-section 5, busbar 7 (at station B,) through the ground to bus-bar 7 at station A, by wire 12 to relay R, wire 14, cord conductor 11, jaek-thimble j conductor 20, the sleeve of lug P the thimble of jack J and thence y wire 25 to the bus-bar 5. The relay R thereupon throws over its armature r and lights the lamp If, indicating to the A" operator that the plug P has been inserted in the Wanted line-jack. It will be observed that this operation is exactly the same as if the A operator had inserted her calling-plug P directly into the wanted jack. The A operator then proceeds toring up by means of the key K, precisely the same as in any other case. I hen subscriber Y answers by taking down his receiver, the difference of potential existing between his jack-thimble and the intermediate bus-b ar 7 is reversed, because he thereby closes the following circuit: from the jaek-thimble by line-wire 2 to substation Y, back by linewire 1 to the central oflice and through wire 26 to the bus-bar 6. The relay R being connected through conductor 20 on one side and the ground on the other with the jack-thimble 7' and the busbar 7, respectively, the reversal of potential and the consequent reversal in current-flow cause the relay to throw back its armature into inoperative osition, extinguishing the lamp If. This int icates to the A operator that the call has been answered. In this also it will be observed the operation is precisely the same as in making a direct connection without trunking. When the conversation has been terminated and subscribers X and Y have restored their receivers to the hooks, thereby breaking their circuits, both supervisory lamps l1 and L immediately li ht. Relay It is energized at this juncture y current from the batterysection a, while the relay R receives its current from the battery-section b at station B. A operator then clears out by removing all plugs from the jacks. The first result of this is to break the circuits of the relays It and R so that their armatures again assume the LIS position shown, and the lamps L and [A2 become dark, so to remain until their cord-circult is again brought into requisition. The second result is the crossing of the trunk-com ductors 2U 21 in the jack J by the closure ol the spring j upon its anvil j. The plug P being still in the jack J a circuit is thus created for the relay R as follows: battery B, bus-bar 5, wire 25, sleeve j, plug P conductor 20, anvil j, spring j", conductor 21, relay It, tip of plu P jaclospring and wire 26 to bus-bar 6, and back to the battery. Current in this circuit immediately energizes the relay R whose armature r closes the circuit 23 and. lights the lamp 1 This indicates to the B operator that the trunk-line is idle. and should be disconnected.

It will be found that this arrangement of circuits and signals provides for every contin ency that may arise in ordinary practice wit iout in the least complicating the work of either "A or B operators, but rather simplifying the same over the arrangements now in use. Suppose, for example, that the "A operator has received the trunk-number and has inserted the plug P, but the B operator has neglected to complete the connection. Supervisory lamp Li remains dark, and as the A operator has not yet rung the subscriber this gives her an infallible indication, whereupon she may again resort to her instruction circuit 24. This contingency may occur through the B operator misunderstanding or not catching the number, in which case she has only to wait without making the connection, being assured that the A operator will come back on the instruction-circuit when she perceives the connection is incomplete. Again, in making a connection if the A operator should misunderstand the trunk-nuniber, and therefore fail to insert the plug P in the trunk-jack, the trunk o erator would immediately be advised o the fact as soon as she inserted the plug P in the wanted line-jack by the lighting of her lamp L In such case the number would be repeated over the instruction-circuit.

Having thus described our invention, what we claim, and desire to secure by Letters Patent, is-

1. In a telephoneexchange system, two switchboard sections or stations each comprising the following instrumentalities: subscribers line-terminals, plugs and cordcir cuits for interconnecting the same, supervisory-signal devices connected to the cord-circuits, a source of current and connections whereby the supervisory-si nal devices may be operated thereby; toget er with a trunkcircuit interconnecting the switchboard sections or stations, and means whereby in making a connection throu h said trunk from one station to the other, 1; e supervisory signals of the cord-circuit at one station Wlll be operated by the current from the source at the other station, substantially as described.

2. In a telephone-exchange system, two central stations, a common battery at each station having end terminals and a grounded intermediate terminal, subscribers lines fed from said batteries, a trunk-line interconnecting the stations and a cord-circuit at one station for interconnecting the lines thcreat with each other or with the trunk-line, means at the other station to interconnect the trunk line with the subscribers lines thereat so arranged as to connect the component linewires at the two central stations in the same order as when interconnected directly at either station, a supervisorysignal device connected between the intermediate batteryterminal and one side of the cord-circuit at the first station, and means at the subscribers stations to maintain their line-circuits closed during the use of their apparatus, whereby the supervisory-signal device will become energized by current from one side or division of one or the other main battery when a direct connection is made or when a trunk connection is completed, and will be deenergized when the called subscriber answers, in either case, substantially as described.

3. In a telephone-exchange system, two central stations, at common battery at each station, subscribers lines fed from said batteries, a trunkdine interconnecting the stations and a cord-circuit for interconnecting the lines thercat with each other or with the trunk-line, means at the other station to interconnect the trunk-line with the subscribers lines thereat, a supervisory-signal device connected with the cord-circuit atthe first station, and means whereby in a direct cord connection between subscribers in the same exchange the supervisory-signal device will derive current from the main battery at said first station, but in making trunk connections the said signal device will derive current from the battery at the other station, substantially as described.

4-. In a telephone-exchange system two central stations, a trunk-line extending between them together with subscribers lineterminals adapted to be connected through the trunk, a circuit-closer at the first station normally maintaining the two sides of the trunk directly closed together, a signal device included in the trunk at the second station, a battery at the second station, and means becoming operative upon completing connection with a subscribers line to bring said battery into connection with the trunk, substantially as described.

5. In a telephone-exchange system, two switchboard stations or sections with subscribers lines terminatin at each and a trunkline extendin between t e sections, a signaleircuit forme in part of the trunk-line, a cir- IOC IIO

cuit-closer at the first section normally maintaining said signal-circuit in signaling condi tion but operable to change said condition when a line is connected to the trunk, a si al device at the second section in said circuit, a source of current-supply also at the said second section or station, and means to connect the same to the signal-circuit when the trunkline is connected finally to the subscribersline, substantially as described.

6. In a telephone-exchange system two switchboard stations or sections, subscribers lines on each, a trunk-line between the stations, a circuit-closer at one station for the trunk actuated in making connection therewith, a signal device connected to the trunk at the other station, a battery also at the other station, and means to connect said battery to the trunk in connecting the latterwith the subscribers line, whereby the signal is normally inactive, but during connection is under the control of the initiating or subscribers operator, substantially as described.

In testimony whereof we have, hereunto set our hands, in the presence of two subscribing Witnesses,this 19th day of October, A D.

JACOB VV'ILLIAM LATTIG. CHARLES LANE GOODRUM.

Witnesses:

L. A. POTTEIGER, M. S. Lnwis. 

